Weighing scales – Self-positioning – Repositioning in response to deflection under load
Patent
1991-05-08
1994-11-22
Fuller, Benjamin R.
Weighing scales
Self-positioning
Repositioning in response to deflection under load
177210EM, 177243, G01G 138, G01G 314
Patent
active
053671287
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to an electromagnetic balance-type weighing apparatus for measuring the weight of an object of weighing by detecting a signal designed to automatically generate an electromagnetic force by means of an electromagnetic coil to offset the displacement of the weighing pan (or balance beam) of the apparatus caused by the weight of the object of weighing and, more particularly, it relates to an improvement realized on such a weighing apparatus for fast-responsiveness, enhanced accuracy and hence high reliability.
2. Background Art
Weighing apparatus of a conventional differential transformer type and load cell type used in various manufacture and process lines for weighing articles (works) have gradually been replaced by those of electromagnetic balance-type as disclosed in U.S. Pat. No. 4,300,647.
The configuration of a known typical electromagnetic balance-type weighing apparatus is shown in FIG. 4 of the accompanying drawings.
In FIG. 4, reference numeral 1 generally denotes a weighing pan/balance beam assembly supported at fulcrum S selected to show a given leverage, the weighing pan being positioned at one end portion 1a of the balance beam for determining the weight of object w placed on it, reference numeral 2 denotes a circular hole provided at a bent-down section of the other end portion 1b of the balance beam of the assembly 1 and reference numeral 3 denotes a light emitter that emits beams of light toward the hole 2, while reference numerals 4 and 5 respectively denote upper and lower light sensors arranged to receive the beams of light passing through the hole 2.
Also, in FIG. A reference numeral 6 denotes a differential amplifier for detecting the difference between the beams received by the light sensor 4 and those received by the light sensor 5. Reference numeral 7 denotes a proportional integral derivative (hereinafter referred to as PID) operation unit for performing the operation of scalar multiplications, integrations and differentiations on the differential signal it receives and sending out a control voltage determined on the basis of the received signal and reference numeral 8 denotes a driving amplifier for generating a driving voltage corresponding to the received control voltage in order to produce a large electric current.
Reference numeral 9 denotes an electromagnetic (force) coil designed to pull the other end portion 1b of the balance beam opposite to the weighing pan downward by means of the electromagnetic force generated by the electric current running through it in accordance with the driving voltage, reference numeral 10 denotes a buffer amplifier for transmitting the voltage generated at resistor R by the electric current running through the electromagnetic coil 9 and reference numeral 11 denotes a low-pass filter (hereinafter referred to as LPF) for producing a DC voltage signal corresponding to the weight of the object of weighing obtained by removing those components of the signal transmitted from the buffer amplifier 10 that are responsible for oscillation and noise.
When the weighing pan 1 of an electromagnetic weighing apparatus having a configuration as described above is displaced clockwise by the weight of an object being weighed, a differential signal is generated by the difference of the amount of light received by the light sensor 5 and that received by the sensor 4, the former now being larger than the latter, so that consequently the control voltage transmitted from the PID operation unit 7 is increased to generate a force to move the weighing pan 1 counterclockwise to restore its initial position and hence the balanced condition of the weighing pan 1.
Since the force of pulling down the end of the balance beam opposite to the weighing pan generated by the electromagnetic coil 9 is linearly proportional to the driving current. The voltage present at the opposite end of the resistor R when the weighing pan 1 is balanced is a linear function of the weight of the object being weighed.
Thus, the we
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Fujimoto Hideya
Horikoshi Kazuhiko
Kikuchi Kunio
Tanaka Osamu
Tsukasa Fumihiro
Anritsu Corporation
Fuller Benjamin R.
Gibson Randy W.
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